The invention relates to an infusion device intended for implantation in a living body, said infusion device being comprised of a device housing implantable in the patient's body having a reservoir for infusion fluid and having a conveying and dosing unit for conveying the fluid from the reservoir to the discharge opening of a catheter.
An infusion device of the type initially cited is known, for example, from the U.S. Pat. No. 4,191,181. For safety reasons the infusion fluid in the reservoir of the device is kept under a pressure which is lower than the pressure at the discharge opening of the catheter. Such a measure prevents fluid from discharging out of the reservoir into the patient's body due to a leak in the capsule or pump. In order to execute this measure, for example, a flexible fluid reservoir is charged by a vapor pressure of such a substance as has a corresponding pressure at body temperature. It is also possible to fill a buffered gas into the tightly encapsulated device housing under such a pressure that, taking the gas equation into consideration, an under-pressure in comparison to the pressure of the environment is still maintained even given a full fluid reservoir.
A hermetic encapsulation of the device housing given maintenance of under-pressure over longer times, however, also produces a series of problems. For example, temperature fluctuations and external changes of air pressure which can change the pressure differential between the body tissues and the inside of the housing must be taken into consideration. As a result, one must proceed from a relatively great under-pressure, for example up to 0.5 bar. The consequence of this, however, specifically given employment of roller pumps as the conveying and dosing unit, is that the danger of a reflux of fluid in the catheter exists during disengagement of the successive pump rollers from the fluid conveyor tube.